osplack



Feb. 21, 1956 J. .1. OSPLACK ABRASIVE WHEEL DRESSER 3 Sheets-Sheet 1 Filed Nov. 30, 1953 INVENTOR Joseph J. Osplock ATTORNEYS FIG. 2

Feb. 21, 1956 Filed Nov. 30, 1953 J. J. OSPLACK ABRASIVE WHEEL DRESSER FIG. 3

5 Sheets-Sheet 2 INVENTOR BY Joseph J. Osplock ATTRNEYS Feb. 21, 1956 J. J. OSPLACK ABRASIVE WHEEL DRESSER 3 Sheets-Sheet 3 Filed Nov. 30, 1953 g Cay/a1 ATTbRNEYS ABRASWE WHEEL DRESSER Joseph J. Ospiack, Detroit, Mich, assignor to Vince Corporation, Detroit, Mich, a corporation of Michigan Application November 30, 1953, Serial No. 394,993

3 Claims. (Cl. 125-11) This invention relates to dressers for abrasive grinding Wheels and more particularly to a tool adapted to dress arcuate profiles on the cutting faces of abrasive wheels employed in grinding curved surfaces.

The technique of forming curved surfaces of mass produced machine parts by grinding the surfaces to the desired shape with contoured abrasive'grinding wheels is rapid and accurate. However, the matter of initially dressing the grinding wheel to the proper contour and of dressing the wheel to re-establish the contour after it has been worn beyond acceptable limits of accuracy is time consuming and, using present methods of dressing abrasive wheels, makes accurate duplication of contours dependent to a very large extent upon the skill of the operator.

I have invented a grinding wheel dressing apparatus which may be rapidly and accurately set up to dress arcuate profiles on abrasive grinding wheels and which will duplicate a given profile any number of times with a high degree of accuracy. No special skill or judgment is required to adjust my new dressing apparatus to produce any specified profile within its range; rather all necessary adjustments are made with standard machine shop techniques using only well known measuring instruments. Furthermore, once set up to produce a particular profile, a single pass of the dressing tool sufiices accurately to form the desired profile, thus eliminating the cut and try techniques presently known wherein a skilled operator must make an approximate cut, compare the profile with an appropriate gauge, refine the adjustment of the dresser, and make further approximating cuts until the desired profile is established within acceptable limits of accuracy.

The principal feature of my invention is the provision of an apparatus which causes a diamond-pointed dressing tool to follow an arcuate path which consists of motion along a basic circular are upon which is superimposed motion along a second circular arc in the same plane as, but not concentric with, the first arc. Displacement of the diamond point along the second arc is precisely controlled as it is simultaneously displaced along the first arc. The resultant path is an are which approximates a segment of a theoretically exact curve to a high degree of accuracy. Thus, if it is desired to dress the profile of an abrasive grinding wheel to be used in grinding the teeth of involute gears, a hypothetical circle may be established for a gear tooth having a given base circle and pressure angle, which hypothetical circle corresponds to the basic circular arc to be followed by the dressing tool. The principles of gear geometry will then determine the amount by which the desired segment of the true involute departs from this hypothetical circle from point to point along it. According to my invention this departure is built into a cam surface which controls the motion of the diamond point along the second are as the point is simultaneously displaced along the basic arc.

nited States Patent As previously stated, the resultant motion is a highly accurate approximation of a segment of a true involute. In accordance with my invention, a tool for achieving this desirable result comprises a frame adapted to support the tool in fixed space relationship to the grinding wheel to be dressed. Journalled in this supporting frame is a first radial member which rotates about a first pivotal axis normal to a plane including the axis of the grinding wheel. Journalled about a second pivotal axis parallel to and remote from the first axis is a second radial member which carries, at a point remote from the second axis, a diamond-pointed dressing tool. Illustrative of the separate motions, it is seen that when the second radial member is maintained in fixed position relative to the first radial member, the diamond-pointed cutting tool may be caused to described a circular are by rotating the first member about the first axis. Similarly, if the first radial member is held stationary and the second radial member is rotated about the second axis, the diamond point is caused to describe yet a second circular arc in the same plane as the first are, but generally oblique thereto.

To relate the departure of the diamond point from the first are along the second arc so that the desired involute motion results as the first and second radial members are simultaneously rotated about their respectives axes, I provide a cam plate fixed to the supporting frame. This cam plate has a basically circular periphery, but a segment thereof is a generally non-circular curve related to the arcuate profile of the gear tooth or other surface to be ground. Means slidably engaging the periphery of the cam plate and operably connected to the second radial member limit the angular displacement of the second radial member with respect to the first radial member according to the departure of the non-circular segment of the periphery of the cam plate from its basic circular contour.

For a complete description of a dressing tool according to my invention, attention is directed to the following description and accompanying drawings in which:

Fig. 1 is a perspective view of a grinding wheel dresser according to the invention;

Fig. 2 is a front elevation of the of Fig. 1;

Fig. 3 is a right side elevation of the grinding wheel dresser of Fig. 1;

Fig. 4 is a left side elevation dresser of Fig. 1;

Fig. 5 is a diagram showing the relation of the geometry of the surface to be ground to the adjustment of the dresser of Fig. 1;

Fig. 6 is another diagram showing the relation of the geometry of the surface to the adjustment of the dresser of Fig. 1.

It will be readily appreciated that all elements of a tool of this nature must be of massive and rigid construction to eliminate the possibility of error-producing deflections and to insure the high degree of accuracy of which my improved dressing tool is inherently capable.

Referring now to Figs. 1 through 4, a grinding wheel 1 to be dressed is mounted on an arbor 2 driven by a suitable electric motor. A supporting frame 3 clamped at its lower end about the arbor bearing, carries a vertical dove tail way 4. Slidably mounted in the dove tail way is a supporting arm 5 which may be moved up and down the way by a lead screw 6 controlled by micrometer knob 7. At the outer end of the supporting arm is a pivot bearing 8 having a vertical axis passing through the axial and radial center of the wheel. Mounted on this hearing for rotation about the vertical axis is a horizontal dove tail track 10 which carries, on a mating dove tail way 11, a pivot arm 12 having a horizontal branch 13 and, depending therefrom, a vertical branch 14. The pivot arm is grinding wheel dresser of the grinding wheel accurately adjustable longitudinally of the track by lead screw 15 controlled by knob 16, and, to assist in determining the position of the pivot arm with respect to the way, I provide a reference surface 17 and a reference button 18. For purposes later to be described, a stop pin 2t) is provided on the supporting arm to engage positioning pins 21 and 21' located on the underside of the dove tail track as the track is rotated about the vertical axis of the pivot bearing. These positioning pins are so located that their engagement with stop pin 20 limits the rotation of the track 10, and consequently of the pivot arm, to precisely 180; at either extreme of this rotation as determined by the pins 21 or 21 engaging the pin 20 the track is exactly parallel to the axis of the arbor 2 and wheel 1.

Fixed to the lower end of the vertical branch 14 of the pivot arm 12, there is provided a horizontal shaft 22 on which is journaled a first radial member 23. The axis of shaft 22 I shall call the first pivotal axis, and it is to be normal to a plane including the axis of arbor 2 when the pivot arm is in either of its stopped positions.

Parallel to this first shaft, but remote therefrom is a second shaft 24 journaled in the first radial member. The axis of this second shaft I shall call the second pivotal axis. One end of the second shaft has fixed thereto a second radial member 25 carrying a cutting tool bracket 26. This bracket has adjustably secured thereto by set screws 27 a cutting tool 28 having a diamond point 30. The proportions of the radial members 23 and 25 and the bracket 26 are such that the point 30 of the cutting tool lies in a plane including the axis of the arbor and wheel when the pivot arm 12 is in either of its stopped positions; moreover, the arc described by the point 30, due to rotation of the second radial member about the second shaft, intersects the first pivotal axis.

Proper coordination between the rotation of the second radial member with respect to the rotation of the first radial member is obtained with elements best shown in Figs. 1 and 3. A fixture plate 31 is fixed with suitable bolts to the first radial member for simultaneous rotation about the first pivotal axis; This plate is conveniently provided with a hand knob 32 to permit the operator of the tool to effect the rotation of the first radial member and the fixture plate.

The fixed horizontal shaft 22 extends through an aperture 33 in the fixture plate 31 and is provided with an axial hole 34 which is threaded to receive the bolt 35. This bolt adjustably secures a cam plate 36 to the end of the shaft 22.

The periphery of the cam plate constitutes the cam surface which controls the angular displacement of the second radial member 25 about the second pivotal axis. Operative connection between the periphery of the cam plate and the shaft 24, to which the second radial member 25 is fixed, is obtained through a train of pivoted members so constructed as to reduce the amplitude of the radial variations of the cam periphery by a suitable factor, 1/11, which may be adjusted within the physical limits of the train of members.

A cam arm 37 pivoted about a screw 38, threaded into the fixture plate, carries a cam follower 40 which is a cylinder clamped in the arm to afford accurate line contact with the peripheral surface of the cam plate 36. The cam arm 37 is also provided with a shelf 41 which is slidably engaged by knife-edged follow finger 42 of ratio arm 43 which is fixed to that end of shaft 24 extending through fixture plate 31. This ratio arm comprises the body 44, provided with reference surface 45, and an adjustable extension 46, provided with a reference surface 47. The distance between these surfaces 45 and 47, that is the overall length of the ratio arm, may be closely controlled by the knob 43 on a lead screw connecting the body 44 of arm 43 and its extension 46.

The follow finger 42 of the ratio arm is maintained in firm engagement with shelf 41 by tension spring 51 connected between the arm and a pin 52 mounted on the plate 31, and the cam follower 40 is maintained in firm engagement with the cam periphery by tension spring 53 con nected between cam arm 37 and the pin 52.

As shown in Fig. 3 the cam plate 36 has a generally circular periphery, the true circular portion serving as a reference in the adjustment of the apparatus which will be explained in greater detail below. However, segment AA of the periphery of the cam plate is in this particular example a curve related to an involute having a specified base circle and pressure angle as illustrated in Figs. 5 and 6.

According to my invention it is possible to utilize a circle of radius Ty the radius of curvature at the point corresponding to pressure angle c of an involute of base circle diameter Dbc, as a first approximation to the true involute which will then lie partially within and partially without this hypothetical circle. The departure of the true involute from the hypothetical circle at succeeding points along the latter are then multiplied or magnified by a. suitable factor, n, and so magnified, are machined into the periphery of the cam as segment AA. The obvious result of this procedure is that the unavoidable errors which arise in the course of machining of the curve bear the relation of l/n to the actual departure of the involute from the hypothetical circle. t is then apparent that the reduction by the factor 1/11 of the magnified departure to the actual and desired departure through the train comprising the cam follower arm 37, the ratio arm 43, and the second radial member 25 results in a reduction of the inevitable machining errors by a factor of l/n. The salutary efiect of these factors on the accuracy with which the diamond point dresses the wheel is at once apparent.

I have found that only a limited number of cam plates are required to enable my new dressing tool to dress abrasive wheels to grind gears having a wide range of base circles and pressure angles. For example, a set of cam plates developed on base circles differing by increments of one quarter of one inch will satisfactorily dress wheels to produce gears having any base circle within the upper and lower limits of the set of cams. Furthermore, I have found that a set of cam plates, all of which are developed for a pressure angle of 20 will accurately dress wheels to grind gear teeth having any other pressure angle. Separate cams can be provided, if desired, for dressing wheels to grind teeth having high pressure angles and relatively long involute rolls. Cams may also be provided for dressing other profiles such as cycloids or composite tooth forms.

Adjustment and operation of my dresser is simple and may be systematized so that the entire procedure of dressing a wheel to grind a specified gear is rapid and accurate. Most of the adjustments are directly related to the geometry of the gear to be ground. This is best illustrated with a particular example. Reference is made to Figs. 5 and 6.

The desired base circle diameter, Db, of the gear to be ground having been specified, the cam plate 36 developed on a nominal base circle diameter, Dbc, nearest to Db is selected. This cam plate is mounted concentric with, and adjustably secured to the fixed shaft 22, with the bolt 35 provided for the purpose, and is rotated until the cam follower 41 engages the true circular reference periphery of the plate which may be conveniently provided at segment B-B in Fig. 3. The actual diameter of the reference periphery of all cams made to be used with a particular dresser will have been selected so that when the cam follower 49 engages the reference periphery, the second radial member 25 is in a. neutral position such that the axis of the cutting tool lies in a horizontal plane containing the first pivotal axis.

The first radial member 23 having been properly positioned, it is preferable to lock it in this position by T=Z D be This reduction ratio is related to the physical dimensions of the dresser in the following manner. The ratio by which the rise and fall of the cam segment A-A is reduced by the cam follower 40 is the ratio of the distance between the axis of the screw 38 and the point of contact of follow finger 42 with shelf 41 (see Fig. 3) to the distance between the axis of the pivot screw 38 and the point of contact of cam follower it). This former distance represented as y may be varied by lengthening or shortening the ratio arm with the knob 48 and lead screw 50 connecting the body and extension; this is the means provided for varying the reduction ratio of the dresser.

It will be apparent that changing the length of the ratio arm also changes the ratio by which motion is reduced by ratio arm 43 and the second radial member 25 which are both fixed to and pivot about the axis of shaft 24. This latter ratio is where 22 is the fixed distance between the axis of shaft 24, i. e. the second pivotal axis, and the axis of screw 38, and la is the perpendicular distance from the second pivotal axis to the center line of tool 28. As previously stated, the first and second radial members of the preferred embodiment are so proportioned that the axis of the diamond holder is intersected by the first pivotal axis. This point of intersection constitutes the center of the basic are described by the diamond point as the first radial member is rotated about the first pivotal axis; the distance between this intersection and the point of the diamond is the radius of the basic are.

It is easily demonstrated that the overall ratio of a train of members of this kind is simply the product of the several reduction ratios, i. e.

is determined for a specified gear and a cam selected as above, the corresponding value of y may be calcu lated numerically. The proper setting of the ratio arm is then expressed as A+y where A is the sum of the distance between the reference surface 45 and the second pivotal axis, the distance between the second pivotal axis and the axis of the pivot screw 38, and the distance from the contact point of follow finger 42 and the reference surface 47. Since this sum is constant for a particular dresser, the ratio arm is easily adjusted to the calculated value of y merely through adjustment, by lead screw 6 knob 48, of the distance between reference surfaces 45 and 47 to equal the sum A+ y.

Following this adjustment of the ratio arm, the spread of the dresser is adjusted to dress the wheel so that it will grind the proper space width between adjacent teeth. This adjustment comprises positioning the center of the basic are at the proper distance from the central plane of the wheel, and is made by advancement or retraction of the pivot arm 12 on the dove tailed track 10 and way 11 by means of knob 16. The reference surface 17 and reference button 18 are accurately located so that the spread may be directly measured between them.

The spread (see Figs. 5 and 6) is given by where Db is the diameter of the base circle of the gear to be ground, c is the pressure angle in radians for which the cam was developed, Inv. (15a is the angle included between a radius of the base circle extended to the origin of the involute at the base circle and the radius of the base circle extended to the point on the involute corresponding to sc and 0' is the angle between the median radius between adjacent teeth and the radius to the point of origin of the involute on the base circle. Where all the cams of a set are formed to the same pressure angle, say 20 as suggested above, the expression may be simplified to where K is the constant sum of the angles (15c and Inv. (Pa for a set of cams developed to the same pressure angle.

The proper radius of the basic arc to be followed by the point is then established by setting the length of the cutting tool 28 from the intersection of its axis with the first pivotal axis to the diamond point equal to the radius of the basic are. This is also the radius of curvature, T as shown in Figs. 5 and 6, of the desired involute at the point corresponding to the selected pressure angle of cam plate 36. The adjustment is conveniently made with the aid of a plate 54 shown only in Fig. 4, temporarily fixed to the reference surface 55 on supporting arm 5 to extend downwardly in front of the diamond point. Then the total distance between the center of the basic arc and the surface 55a of the plate is equal to the sum of the spread, which was previously computed, plus the fixed distance between the center of pivot bearing 8 and the surface 55a of the plate 53. The setting is made by the advancement or retraction of the cutting tool 28 in the bracket 26 so that the distance between the diamond point 30 and the surface 55a of the plate 54 is equal to the sum set out less the desired radius of the basic arc.

The next adjustment is to angularly position the segment AA of the cam with respect to a horizontal reference which will determine the point along the basic are at which the diamond point will begin to be displaced along the second are. This angular position is determined by the space semi-angle, a, referred to above and the cam plate is conveniently adjusted to this angle with the aid of sine buttons 56 and 57 accurately located on the face of the cam plate 36 with respect to segment AA. A surface having a slope equal to the angle, 0', with respect to the horizontal is placed in contact with both sine buttons to effect the adjustment of the cam plate and then bolt is tightened to hold the cam plate in the adjusted position. The cam plate is fixed in this adjusted position and does not rotate about the axis of the shaft 22 during the Wheel dressing operation to be described below.

Finally the dresser is accommodated to the diameter of the particular wheel to be dressed by the lowering or raising of the supporting arm 5 with lead screw 6, and the dresser is then ready to form the profiles of the wheel,

7 The first face is dressed by the drawing of the fixture plate knob 32 downwardly to rotate the first radial member about the first pivotal axis while the abrasive wheel is turning.

As the knob 32 is pulled downwardly the plate 31 rotates about the axis of the shaft 22 which causes the cam follower 40 to be moved over the segment AA of the cam 36. Since the radius of segment AA varies from point to point, the cam arm 37 is caused to rotate about the screw 38. This rotation causes a rotation of the surface 41 of arm 37 about screw 38 which surface is engaged by the follow finger 42 thereby proportionally transmitting the rotation of the cam arm 37 to the ratio arm 43. The ratio arm 43 being fixed through the shaft 24 to the second radial member 25 carrying the tool 36, the displacement of the cam follower 49 as it traverses the segment A--A of the cam plate 36 is ultimately transmitted to the tool tip 30. Simultaneously with the motion just described, there is also imposed on the tool tip an arcuate motion due to the rotation of the first radial member 23 about the axis of the shaft 22, which axis if extended would pass through the body of the cutting tool 28. It is now apparent that the motion of the tip of the cutting tool is comprised of two superimposed basic arcs which describe one half of the desired profile of the Wheel being ground. The first of these basic arcs is a circular one due to the rotation of the cutting tool 28 about the axis of the shaft 22. That this is a circular arc can be clearly seen if it is momentarily assumed that the segment AA of cam 36 is circular about the axis of the shaft 22 so that no rotation of the cam follower arm is effected as the knob 32 is pulled downwardly to rotate the fixture plate 31 about the axis of the shaft 22. The second arc is due to displacement of the cam follower as it traverses the segment A-A of the cam plate 36 and is an are which is essentially oblique to the circular are just described; that is, as the tool tip 30 moves through the first described circular are centered about the axis of the shaft 22 it simultaneously is displaced obliquely to this circular are by the rotation of the second radial member about the axis of the shaft 24. In one pass of the diamond point the profile is dressed and then the knob is returned to its upper position. To dress the profile on the other face of the wheel, the pivot arm 12 is turned about the axis of the pivot bearing until the stop pin 20 engages the positioning pin 21 to position the dresser relative to the other face. Since every member of the dresser is precisely located with respect to the central plane and an axial plane of the wheel, and the axis of the pivot bearing 8, about which the pivot arm 12 is rotated, passes through the center of the wheel, the diamond point has precisely the same relation to the face of the wheel now to be dressed as it had to the face just dressed and no other adjustment is required. This second face is dressed by drawing the knob 32 down again. This completes the dressing operation and the wheel is now ready to grind tooth profiles into gear blanks.

From the foregoing description it will be readily appreciated that I have invented a grinding wheel dressing apparatus which greatly simplifies the matter of dressing grinding wheels to non-circular profiles with the degree of accuracy required by modern practice. Furthermore, it is seen that the present time consuming method of dressing abrasive wheel profiles by making a succession of approximate cuts with a dressing tool has been replaced by apparatus which, requiring only a limited number of adjustments, will dress a profile to a desired form with one pass of the dressing tool and which will accurately duplicate the same profile any number of times.

I claim:

1. Grinding wheel dressing apparatus comprising in combination a supporting frame, a first radial member journalled in said frame for rotation about a first axis, a second radial member journalled in said first member for rotation about a second axis parallel to and remote from said first axis, a dressing tool having a dressing tip and being fixed to said second member at a position remote from said second axis, a cam plate fixed to said frame and normal to said first axis, the periphery of said cam plate having a contour related to the desired contour of the wheel to be dressed, and means engaging the periphery of the cam plate and operatively connected to said second member for effecting a rotation of said second member about said second axis as said first member is rotated about said first axis, which rotation of said second member is related to the departure of the peripheral contour of the cam from an are which is circular about said first axis whereby, when said supporting frame is placed adjacent a rotatably mounted wheel to be dressed with said first axis normal to a plane including the rotational axis of the wheel, said tool tip is in engagement with the periphery of the wheel.

2. Grinding wheel dressing apparatus comprising a frame fixed adjacent a rotatably mounted grinding wheel to be dressed and having a supporting arm parallel to the axis of the wheel and adjustable radially of the Wheel, a pivot on said arm having its axis parallel to a radius of the Wheel, a pivot arm mounted on said pivot for rotation precisely to either side of an axial plane of the wheel and being adjustable axially of the wheel, a first radial member mounted on said pivot arm for rotation about a first axis normal to a plane containing the axis of said pivot, a second radial member mounted on said first member for rotation about a second axis parallel to said first axis and removed therefrom, a dressing tool fixed to said second radial member, the tip thereof lying in an axial plane of the wheel when said supporting arm is precisely 90 on either side of an axial plane of said wheel, a cam plate fixed to said supporting arm normal to said first axis and having a non-circular peripheral contour related to the desired profile of the wheel, a follower arm pivoted on said first radial member about an axis parallel to said first axis, a portion of said follower arm engaging the periphery of said cam, a variable length ratio arm operatively connected to said second radial member for rotation therewith about said second axis, a portion of said ratio arm remote from said second axis slidably engaging a portion of said follower arm remote from said third axis.

3. Apparatus for dressing involuteprofiles on a grinding wheel comprising, in combination, a spindle for a wheel to be dressed, a frame adapted to be mounted in fixed spaced relation to said spindle, a supporting arm slidably mounted in said frame, means for adjusting said supporting arm vertically, a pivot on said arm having a vertical axis, a pivot arm mounted on said pivot and adapted to rotate precisely 90 to either side of a plane including the axis of the spindle, means for adjusting said pivot arm normal to the axis of said pivot, a first radial member journalled in said pivot arm for rotation about a horizontal first pivotal axis, said first pivotal axis being normal to a plane containing the axis of the spindle when said pivot arm is rotated precisely 90 to either side thereof, a second radial member journalled in said first radial member for rotation about a second pivotal axis parallel to said first axis and removed therefrom, a dressing tool fixed to saidv second radial member, a. cam plate fixed to said supporting arm normal to and angularly adjustable about said first pivotal axis, said cam plate having a non-circular peripheral contour related to the desired involute profile of the wheel to be dressed, a cam follower arm pivoted on said first radial member about an axis parallel to said first pivotal axis, a portion of said follower remote from said cam follower axis engaging the periphery of said cam plate, a variable length ratio arm operatively connected to said second radial member for rotation therewith about said second pivotal axis, a portion of said ratio arm remote from said second pivotal axis slidably engaging a portion of said follower arm remote from said cam follower axis, whereby manual 9 10 a rotation of said first radial member about said first pivotal scribe the non-circular arc to which each of the opposed axis causes pivoting of said follower am about said cam profile O a Wheel s to b dressedfollower axis in accordance with the departure of the periphery of said cam from an arc circular about said References Clted 1n the file of thls Patent first pivotal axis, which pivoting of said follower arm is 5 UNITED STATES PATENTS proportionately transmitted by said ratio arm to said 2 326 795 osplack Aug 17 1943 Second radial member to superimpose on the circular mo- 2:358:39? Grave Sept. 1944 tion of the tip of said tool induced by rotation of said first radial member a motion normal to said circular mo- FOREIGN PATENTS tion, the combined motions causing said tool tip to de- 10 230,487 Great Britain Mar. 8, 1928 

